Projectile with an incorporated dielectric-loaded cavity antenna



June 30, 1970 H. s. JONES. JR

PROJECTILE WITH AN INCORPORATED DIELECTRIC-LOADED CAVITY ANTENNA Filed March 28, 1968 INVENTOR HOWARD S. JONES, JR.

I ZW? BY m4 #W) a! 9 ul ATTORNEYS 610.1 Qua J United States Patent 01 ice Patented June 30, 1970 US. Cl. 343-708 7 Claims ABSTRACT OF THE DISCLOSURE A projectile having a telemetry system built-in which requires an antenna which is structurally incorporated in the outside casing of the projectile. A dielectric is coated with a thin layer of copper and is shaped to the dimensions of a cavity waveguide antenna. The coated dielectric is cylindrically shaped to conform to the wall structure of the projectile. The dielectrically loaded waveguide cavity antenna has sufiicient structural strength to act as the wall structure of the projectile or as a portion of the wall structure. The metal coating on the dielectric is cut or etched away to expose a dielectric window on the exterior of the projectile so that the signal may be transmitted from the antenna to a receiver.

The invention described herein may be manufactured, used, and licensed by or for the Government for governmental purposes without the payment to me of any royalty thereon.

BACKGROUND OF THE INVENTION Since the advent of projectiles utilizing proximity fuzing systems, telemetry, missile guidance, and other types of electronic communications a problem in the design of such systems has been to provide an antenna which is small, compact, and will not take up too much space within the projectile. This is especially important where the projectile has a fixed size, i.e., a mortar or artillery shell and where space and weight limitations are critical problems in the design of self-contained fuzing and telemetry systems. Another problem has been to construct antennas in small diameter bodies which can handle signals at the lower microwave frequencies (800 to 2500 mHz.) and which would lend themselves to multi-element construction. It is also important that the electrical characteristics of these antennas meet design specifications. This normally means that the antenna must have certain specified radiation pattern characteristics, impedance matching, and sufficient bandwith and gain to fulfill the telemetry function.

Prior systems used in artillery shells, bombs, and other military hardware have utilized small antennas which are usually mounted in the nose structure of these projectiles. Many of these small diameter (2 to 6 inch) devices have cylindrical and conical wall structures which have normally provided a casing for the electronics and explosives. The antennas used in prior systems normally utilized radiating elements such as loops, stubs and ring networks that were inclosed by the dielectric nose-cone or body of the projectile. These elements have proven to be far less efiicient, more difficult to design and construct, and also more costly to produce than would be desired for such antenna systems. While many of the electrical characteristics desired could have been obtained with the use of cavity waveguide antennas, these antennas could not be used because of their extremely large size and heavy weight which has been inherent in the design of such antennas.

It is therefore an object of this invention to provide a projectile with an antenna system that uses a minimum of space within the projectile.

It is another object of this invention to provide a small compact antenna system for a projectile which is efficient in its electrical characteristics and yet it is extremely light weight.

Still another object of the invention is to provide an antenna for a projectile which can be incorporated as a part of the wall structure of the projectile Still yet another object of the invention is to provide an antenna system for projectiles which man be easily constructed, and is inexpensive to manufacture.

SUMMARY OF THE INVENTION The aforementioned and other objects are attained in a projectile having incorporated within its wall structure a cylindrical dielectric-loaded cavity antenna. The antenna is constructed of a dielectric with a relatively high dielectric constant and is coated with a metallic coating sulficient to carry an RF current. The coating is removed to leave the dielectric exposed at selected areas, thus forming a window through which the electromagnetic waves can propagate from the antenna. The plated dielectric is shaped to the dimensions of a waveguide cavity antenna and bent into a cylindrical shape so that the antenna can act as part of the wall structure of the projectile. By using certain dielectrics which have sufficient structural strength, the antenna can constitute the entire or a portion of the projectile wall without sacrificing any of the structural integrity of the projectile.

BRIEF DESCRIPTION OF THE DRAWINGS The specific nature of the invention, as well as other objects, aspects, uses and advantages thereof, will clearly appear from the following description and from the accompanying drawing, in which:

FIG. 1 is an illustration of the projectile having an antenna incorporated therein in accordance with my invention.

FIG. 2 shows a dielectric loaded cavity antenna in accordance with my invention.

FIG. 3 shows a dual cavity dielectric filled cavity antenna in accordance with my invention.

FIG. 4 shows still another dielectric filled loaded cavity antenna in accordance with my invention.

DESCRIPTION OF THE PREFERRED EMBODIMENT In FIG. 1 the antenna 12 of my invention is shown mounted in an unmodified mortar shell 10. The antenna 12 can be mounted at any point in the length of the projectile; however, normally due to the fact that most of the electronics circuitry in the projectile will be mounted near to the nose, the antenna would also be mounted near the signal producing circuitry to simplify construction and electrical connections between the antenna and circuitry. In the figure the antenna 12 is shown mounted on a sleeve between the active fuze or telemetry equipment 14 and the body of the shell 11. It should be readily apparent from the drawing that no major modification of the shell is necessary, and there are no protrusions or projections from the shell which will in any way affect its performance.

In FIG. 2 there is shown an embodiment of a cylindrical dielectric-loaded cavity antenna 20' before being mounted in a projectile. The antenna 20 has an antenna core 22 which is a dielectric cylinder 1.75 inches high and 2.35 inches in outer diameter, with a .250 inch wall thickness. The wall of this antenna is cut at one point 30 along its length, leaving a .010 inch separation at the ends.'The purpose of this open slot is to define the end boundaries of the waveguide. The dielectric is copper plated with a coating 26 of sufficient thickness to carry the RF current generated within the waveguide. A radiating slot 24 is etched or milled in the copper coating on the exterior surface of the cylindrical cavity waveguide to enable the electromagnetic waves to propagate from the antenna. Energy is fed to antenna 20 through a coaxial cable connector 28. The center conductor of the coaxial cable connector runs through the dielectric and makes electrical contact with the copper coating on the opposite side of the dielectric. This has the effect of a post through the dielectric by which the dielectric may be excited.

A basic concept utilized in the embodiment of FIG. 2 and the following embodiments is that loading a waveguide with a dielectric material will allow reduction in the dimensions of the waveguide by a factor of the /e where s is the dielectric constant. However, this reduction in physical size is accompanied by a narrowing of bandwith.

The dielectric selected must not impair the structural strength of the projectile. Some dielectrics having sufficient strength for use with my invention are epoxy, silicone-fiber-glass, Teflon, and FPO. A dielectric-loaded cavity waveguide antenna coated with metal is further described in my copending application entitled Copper Plated Foam Dielectric Antenna and Waveguide Components and Method of Making the Same, Ser. No. 482,955, filed Aug. 26, 1965.

In FIG. 3 another embodiment of a cylindrical dielectric-loaded cavity antenna is shown. The antenna 32 is constructed in a manner similar to the antenna shown in FIG. 2. In this embodiment the antenna has a radiating slot 34 etched or milled in the copper surface as shown. An input feed 38 is constructed as in FIG. 2 through which a coaxial input is attached to the antenna. However, instead of having an open slot 30 as in FIG. 2, the antenna 32 has a hole 36 drilled through the dielectric and which is copper plated therethrough. It has been found that the hole 36 has the same short circuit effect as the open slot 30 in FIG. 2. The hole 36 sufficiently defines a vertically aligned short circuit in the dielectric of the antenna to electrically define a cavity waveguide antenna. Any minor insufficiencies in the electrical characteristics of the antenna 32 are more than offset by the ease of manufacture and the cost factors in construction. This antenna has the added advantage of greater structural strength due to the fact that there is no break in the dielectric.

FIG. 4 shows a cylindrical dielectric loaded cavity antenna which has a single dielectric comprising two separate antennas. The dual cavity antenna 40 shown has a cylindrical dielectric core similar to the previous embodiments, and is similarly copper coated. In order to define the dual cavities, two series of plated-through holes 42 are drilled in opposite sides of the cylindrical dielectric core. Since these holes have the effect of acting as a short circuit in the dielectric, two cavities 46 and 48 are defined by the holes. It is then possible to have two radiating slots 45 and 47 which may be polarized in opposite planes. As shown in the figure, radiating slot 45 is vertically polarized and radiating slot 47 is horizontally polarized. While not shown for purposes of simplicity, it should be understood that each cavity 46 and 48 would have an input signal connected to the respective cavity by a coaxial input connector similar to the one described for FIGS. 2 and 3.

It should be realized that not only is it possible with my invention to have part of the body casing utilized as the antenna, but it is also equally feasible to use the nose cone or any other structural part of the projectile body as the antenna. Use of the nose cone as an antenna is especially attractive, because nose cones are normally made. of a dielectric material. All that is necessary to utilize such a nose cone as an antenna is to copper coat it and provide a radiating slot and an input feed.

In situations where it becomes necessary to vary the squint angle or the direction of energy radiation relative to the axis of the projectile, several antennas can be mounted in the projectile body and phased in such a manner as to obtain the desired radiating characteristics.

By using my invention it is therefore possible to provide an antenna for a projectile which does not use any of the space within the projectile, is extremely light, very inexpensive, easy to manufacture and provides electrical radiating characteristics superior to prior systems.

I claim as my invention:

1. In combination with a projectile of the class wherein a signal generated within the projectile is to be transmitted from an antenna in the projectile, the improvement comprising:

(a) a dielectric material shaped to the inner dimensions of a circular waveguide cavity antenna which is adapted to be a part of the exterior wall structure of the projectile;

(b) a metallic coating deposited on the dielectric of a thickness sufficient to conduct the RF current of an electromagnetic wave propagating through the waveguide;

(c) short circuiting means which together with the metallic coating defines a cavity waveguide antenna, window means in the metallic coating at some selected area on the exterior surface of the dielectric so that electromagnetic energy may be transmitted from the cavity waveguide antenna, and

(d) means for connecting an input signal to the cavity waveguide antenna.

2. The combination of claim 1 wherein the short circuiting means is an open slot in the dielectric material which is covered with the metallic coating.

3. The combination of claim 1 wherein the short circuiting means is a single hole in dielectric material which is covered throughout with the metallic coating.

4. The combination of claim 1 wherein the short circuiting means is a plurality of holes in the dielectric material which are covered throughout with the metallic coating.

5. The combination of claim 1 wherein the dielectric material has a dielectric constant substantially higher than that of air.

6. The combination of claim 5 wherein the window means is a slot-shaped hole cut in the metallic coating so that the dielectric material is exposed on the surface of the projectile.

7. The combination of claim 6 wherein the metallic coating is copper.

References Cited UNITED STATES PATENTS 2,761,137 8/1956 Van Atta et al. 343-771 3,346,865 10/1967 Jones 343-771 ELI LIEBERMAN, Primary Examiner T. J. VEZEAU, Assistant Examiner U.S. Cl. X.R. 343-77l, 785 

